Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.80   5.317%   $62.9796   $62.98   $63.00   $63.00  
  Purchase #2 $191.34   4.148%   $199.2768   $199.28   $199.30   $199.30  
  Purchase #3 $127.94   8.496%   $138.8098   $138.81   $138.80   $138.80  
  Purchase #4 $187.59   6.135%   $199.0986   $199.10   $199.10   $199.10  
  Purchase #5 $24.44   13.124%   $27.6475   $27.65   $27.65   $27.60  
  Purchase #6 $10.75   8.561%   $11.6703   $11.67   $11.65   $11.70  
  Purchase #7 $76.32   12.451%   $85.8226   $85.82   $85.80   $85.80  
  7 purchase totals = $678.18       $725.3052   $725.31   $725.30   $725.30